The research is directed to the identification and characterization of the enzymes, principally the microsomal mono-oxygenases, which metabolize natural as well as foreign compounds in insects. All life stages of the house fly, M-domestica, the flesh fly, S. bullata, and the blow fly, P. regina are being investigated. For the most part the enzymes are contained in the microsomal pellet or supernatant fraction of insect homogenates. During the next grant period efforts will be concentrated on the solubilization of cytochrome P-450, its resolution into chemically distinct forms, its induction by exogenous chemicals, its comparative level in insecticide resistant and susceptible strains, and its level throughout the life stages of the three species.